Novel high εr MNdTiNbO7 (M = Ca, Sr) microwave dielectric ceramics: preparation, phase composition, microstructure, and dielectric performance

MNdTiNbO7 (M = Ca, Sr) ceramics were prepared by a conventional solid-state reaction method. Single-phase dense CaNdTiNbO7 (CNTN) ceramic was obtained at 1400 °C and displayed outstanding microwave dielectric properties of Q × f = 6710 GHz, τf = 205 ppm/°C, and εr = 65.1. While the excellent microwave dielectric properties of Q × f = 8088 GHz, τf = 305 ppm/°C, and εr = 56.5 were obtained for the SrNdTiNbO7 (SNTN) ceramic at 1375 °C. The GSAS analysis software was used to investigate the ion occupancy of the ceramic samples and the changes in their phase structure. When the sintering temperature was 1400 °C, the lattice energy and packing fraction of the CNTN ceramic reached the maximum values of 41,779.7 kJ/mol and 65.35%. The CNTN ceramic resistance is mainly influenced by the grain boundaries. The substitution of Ta for Nb could adjust the τf value of CNTN ceramic. As x = 0.8, the τf values of CaNdTi(Nb1−xTax)O7 ceramics sintered at 1400 °C would be decreased from + 205.18 to + 20.27 ppm/°C.